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<p class="msipheader7557e74b" align="Left" style="margin:0"><span style="font-size:9.0pt;font-family:Arial;color:#317100">PUBLIC</span></p>
<br>
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">I’m writing a type checker plugin that should do things whenever used in the context of a module that already has some definitions loaded. I’ve hacked together the following
function using internal details that I feel I should not be using:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">lookupOrigMaybe :: Module -> OccName -> TcPluginM (Maybe Name)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">lookupOrigMaybe mod occ = do<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> hsc_env <- getTopEnv<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> unsafeTcPluginTcM $ liftIO $ updateNameCache (hsc_NC hsc_env) mod occ $ \cache0 -> do<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> let name = lookupOrigNameCache cache0 mod occ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> return (cache0, name)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">I would like to do this in a nicer way instead. It should be enough to check that the given module is already loaded, since for my use case, if the module is there but the name
isn’t, then all bets are off and my plugin might as well just error out. So I was hoping I could use `findImportedModule` followed by `lookupOrig`, but alas, `findImportedModule` fails me in one of two ways:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-add-space:auto;mso-list:l1 level1 lfo4">
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">If I don’t specify the package (i.e. use `NoPkgQual`), `findImportedModule` seems to return a `Found{}` result even when the module isn’t actually loaded yet, leading to `lookupOrig` failing:<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> attempting to use module ‘main:Cortex.Stem.Relation.Types’ (Cortex.Stem.Relation.Types) which is not loaded</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="2" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-add-space:auto;mso-list:l1 level1 lfo4">
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">If I do specify the package (using `ThisPkg`), then `findImportedModule` chokes in situations when the given unit would come “later” in the dependency graph than the currenty processed one:<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">ghc-mu-core-to-exp: panic! (the 'impossible' happened)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> GHC version 9.5.20220830:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> findImportModule<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">Cortex.Stem.Relation.Types<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">"main"<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">Just ghc-bignum<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">main<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">[ghc-bignum, cortex-prim]<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">Call stack:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> CallStack (from HasCallStack):<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> callStackDoc, called at compiler/GHC/Utils/Panic.hs:188:37 in ghc-lib-0.20220830-FvKByKwp6ri5ICk6wiQO8W:GHC.Utils.Panic<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> pprPanic, called at compiler/GHC/Unit/Finder.hs:160:32 in ghc-lib-0.20220830-FvKByKwp6ri5ICk6wiQO8W:GHC.Unit.Finder<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">Please report this as a GHC bug:
<a href="https://www.haskell.org/ghc/reportabug">https://www.haskell.org/ghc/reportabug</a></span><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">So my question then, is what is the recommended way of looking up a loaded definition opportunistically from a type checker plugin?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> Gergo<o:p></o:p></span></p>
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